Six species and subspecies of rats and mice, Arvicanthis niloticus, Rattus norvegicus, R. rattus frugivorus, R. rattus alexandrinus, R. rattus rattus, and Mus musculus, were found associated with cotton, wheat, maize, sugar-cane, vegetables, fruit and berseem in the vicinity of Alexandria, Egypt. A. niloticus comprised 42·2% of all species collected. Maize, wheat, cotton and berseem were infested most. The lowest infestation was recorded in the fruit fields. Infestation in sugar-cane and vegetables was intermediate. R. norvegicus, M. musculus, R. rattus frugivorus, R. rattus alexandrinus and it. rattus rattusformed 23·9, 16·7, 10·4, 4·2 and 2·7% of the species collected respectively. Of the seven crops investigated, only two (cotton, wheat) were not infested with R. rattus rattus, but all were plagued with some species of rodents. The abundance of these rodents in fields seemed to be positively correlated with temperature and relative humidity. Winter represents a definite off-season for all species recorded.

Six species of fleas (Xenopsylla cheopis, Nosopsyllus fasciatus, Ctenocephalides felis felis, Leptopsylla segnis, Pulex irritans and Echidnophaga gallinacea), three of sucking lice (Polyplax abyssinica, P. spinulosa and Hoplopleura capitosa), five of parasitic mites (Ornithonyssus bacoti, Laelaps echidnina, L. keegani, Androlaelaps zulu and Haemolaelaps sp.) and the tick Rhipicephalus sanguineus sanguineus were recovered from the rodents. Fleas (especially X. cheopis) and lice generally showed a certain degree of host specificity. A close relationship has been shown to exist between the abundance of fleas and lice and the abundance of some rodent hosts and climate. However, no definite host specificity or relation to climate was shown by infestation with mite species. Only B. sanguineus sanguinetie was recovered from S. rattus frugivorus during July, October and December; from R. rattus alexandrinus during November; and from R. rattus rattus during September. Its rate of infestation did not exceed one specimen per rodent host.

Negative calcium and phosphorus balances were produced in two experiments on six horses fed diets containing 2·6 or 4·3% total oxalate. The main calcium and phosphorus loss was in faeces. The urinary loss of calcium was reduced and that of phosphorus increased. A positive balance of magnesium was maintained. No clinically significant changes in blood concentrations of calcium, phosphorus, magnesium or alkaline phosphatase were produced. The bulk of ingested oxalate was unaccounted for in faeces and urine. It is suggested that the intestinal bacterial flora utilized the oxalate. The results supported the hypothesis that dietary oxalate is the cause of equine nutritional secondary hyperparathyroidism which arises when horses graze several tropical grass species.

The response of winter wheat cv. Maris Huntsman to waterlogging was studied in two experiments in soil columns outdoors. Winter waterlogging treatments increased nodal root production and the proportion of aerenchyma within roots, but caused chlorosis and premature senescence of leaves, and decreased tillering. For all treatments, grain losses were much less than expected from the extent of tiller loss in winter; losses after single waterlogging events ranged from 2% (after 47 days with the water-table at 5 cm) to 16% (after 80 days with the water-table at the soil surface). Yield losses after three waterloggings at the seedling, tillering and stem elongation stages of growth were additive, and totalled 19%. In many treatments, grain loss was associated with lighter individual grain weights, suggesting that the size of the root system or efficiency of water and nutrient uptake by roots at the later stages of growth may have been less after earlier waterlogging. The importance of nitrogen fertilizer in maintaining a satisfactory plant nitrogen status was shown when nitrogen was with held before a 3-week waterlogging treatment during stem elongation; tiller and floret survival was subsequently greatly restricted and grain yields decreased 22% below those of plants waterlogged at the same stage of growth but supplied with nitrogen.

The growth in body weight of 91 stags from weaning to 15 months of age and of a smaller number from 15 months to maturity was examined using observations from a farmed stock kept on hill land. Growth rate in winter from 3 months to 10 months of age was proportional to feed allowed and was 35 % greater than for hind calveskept under similar conditions. Growth rate in the subsequent summer was greater for stags than for hinds in sixout of seven instances. After 15 months of age, stags continued to increase in body weight and their weight thus continued to diverge from that of hinds such that at 87 months the average weight of the surviving nine stags was 132 kg and that of the surviving 47 hinds, 78 kg. It is estimated that the equilibrium weight of stags was 154kg.

An experiment to determine the effect of concentration of boron in irrigation water on tissue Ca/B ratio and yield of lentil, barley and oats is described and the results discussed. Tissue Ca/B ratio is a better index for detecting B toxicity in plants. The grain and straw yield of lentil and barley decreased on and beyond 3 and 6, and 6 and 8 mg B/1 in irrigation water, respectively, but there was no effect on green fodder yield of oats.

DNA, RNA and protein concentrations, cathepsin D activity and tritiated thymidine incorporation into DNA were measured in selected muscles from newborn to 7-day-old ‘splayleg’ piglets. The results indicated that the pattern of development differed considerably from that observed in muscle from normal piglets, and the range of results was greater both within and between affected animals. The most striking difference between muscle from normal and ‘splayleg’ piglets was in the incorporation of tritiated thymidine, which was lower in the latter from 3 to 6 days of age, indicating that the number of cells undergoing mitosis may have been reduced. It is suggested that this could have a severe effect on future muscle growth especially if satellite cells are affected.

Growth and yield components of a semi-dwarf spring wheat (Triticum aestivum L., cv. GWO 1809) were determined under three different atmospheric CO2a concentrations (350, 675 and 1000 μ1/1) in controlled environment chambers of the Duke University Phytotron. CO2 enrichment enhanced tiller and head emergence and increased the number of head-producing tillers and the total dry weight of the plants. Total leaf area, stem height and root/shoot ratio of the plants were greater at high CO2 concentrations than at low. Net assimilation rate (NAR) increased with increasing CO2 concentration and decreased with plant size. There was little effect of CO2 enrichment on leaf weight ratio (LWR) and leaf area ratio (LAR) and no significant effect on specific leaf area (SLA). The weight and number of seeds were significantly higher with increasing CO2 concentration. The results of this study provide evidence that important changes in plant growth and development may occur during the next century if global CO2 enrichment continues. Some of these changes would have important ecological impact in natural and managed ecosystems in the future.

The Guadalcanal Plains encompass approximately 460 km2 with both forest and grassland phases. Mean annual rainfall is 2160 mm, with a drier season from June to October, but soil moisture deficits seldom occur. Soils are freely to imperfectly drained brown loam to clays (Ustropepts). Soil analyses show available P concentrations of 15–17 μg/g, adequate K, Cu, Zn and Mn, and high Ca and Mg, but sulphate sulphur is low. A nutrient omission trial gave significant negative responses to the omission of P, K, S and Mo. However, responses to P applications were not obtained in the field with Centrosema pubescens, but significant responses to K and S were found under a cut and remove system. Yield response in the grasses Brachiaria decumbens and B. mutica to applied N was markedly limited in the absence of applied S, even though B. mutica was able to maintain S concentrations in herbage at 2–3 times those of B. decumbens. Without applied S, S contents and N:S ratios in B. decumbens were inadequate for beef cattle, but adequate in B. mutica except at high N inputs (300 kg/ha/year). Application of 40 kg S/ha to the legume C. pubescens increased yields by approximately 50%, reduced incidence of Cercospera leaf spot, and gave increased N concentrations. For establishment of sown mixed pastures on the Guadalcanal Plains we recommend the basal application of 20 kg P/ha, 50 kg K/ha, 30 kg S/ha and 0·15 kg Mo/ha, with 30 kg S/ha applied every 2 years.

A series of experiments investigated mineral supplements for the correction of negative calcium and phosphorus balances in horses fed tropical grass hays containing more than 0·5% total oxalate.

A daily supplement of a soluble calcium source was retained with an efficiency of 60% implying no interference with calcium absorption from supplements by oxalate or other factors in the hays.

The palatability of limestone, rock phosphate, dicalcium phosphate, a limestone and dicalcium phosphate mixture and mono-ammonium phosphate was tested with a view to providing a supplement once weekly. With the exception of the latter, all were consumed readily when mixed with 50–60 % molasses (w/w) and hourly intakes of 200 g calcium and 50 g phosphorus were recorded.

In balance trials using horses fed tropical grass hays, 1 kg of either rock phosphate, or a mixture of limestone and dicalcium phosphate (1:2, w/w), each mixed with 1·5 kg molasses, was fed on the 8th day of a 14-day balance trial. The retention of calcium from the supplements ranged from 19 to 41% and that of phosphorus from 22 to 42%. The passage time for unabsorbed minerals was about 4 days. This amount of supplementation can accommodate calcium and phosphorus losses of at least 20 and 10 mg/kg live weight/day respectively. A supplement of 1 kg limestone overcame a negative calcium balance of 20 mg/kg live weight/day but did not overcome a negative phosphorus balance.

Five calcareous soils (pH 7·3–7·7) designated A-E, deficient in or responsive to Zn and containing Fe in the critical or adequate range, were used in a glasshouse study on maize to assess the effects of P alone or in combination with Mg, Zn or both on the content of Fe in maize.

Overall, P significantly depressed Fe in maize. When Mg was applied to a P or PZn treatment, it either depressed or had no effect on Mg in maize but it significantly (P < 0·001) increased Fe. For the soil where Fe in maize was increased with P treatment, the Zn concentration in the tissue was relatively very low. By contrast, in another exception where PMg treatment depressed Fe in maize, tissue Zn concentration was relatively very high. There was a significant negative correlation (r = –0·45; P < 0·05) between Zn and Fe in maize tops.

A survey of 46 vineyards was conducted to determine whether some nutritional disorder was the cause of declining yields. The surface soils, in general, are alkaline, calcareous, medium to high in organic matter, light in texture and sufficient in available micronutrients except B. Petiole analysis indicated a deficiency of Zn, Fe, Mn, B and Cu in 70, 52, 37, 20 and 13% as well as an excess of P and K in 35 and 93% of the vineyards respectively.

Significant negative correlations of P with Fe and Mn and that of K with Zn showed that the lack of Fe, Mn and Zn might have been induced by excessive application of P and K fertilizers. Poor correlations between the DTPA-soluble concentrations of Cu, Fe, Mn and B in the soils and those in the petioles suggested the nutrient status of surface soils to be of little value in the nutrition of grape vines or that the petiole may not be the best tissue for this purpose.

An experiment was made with growing pigs, to investigate the effect of water restriction in combination with self-fed diets of reduced energy content upon carcass quality.

The diets compared contained 5 and 30% of lucerne hay and the water treatments were ad libitum or progressively restricted amounts during the finishing period (60–90 kg live weight).

Both increasing the proportion of lucerne meal and restricting water intake reduced significantly depth of backfat and the weight of total subcutaneous fat. There was no interaction between the treatments.

The results are discussed in the light of the findings of Cunningham & Friend (1966).

Animal production was compared on three pastures, Brachiaria mutica (para), B. decumbens (signal) and Panicum maximum cv. Hamil (hamil) each sown with a common legume mixture of Centrosemapubescens (centro), Macroptilium atropurpureum cv. Siratro, and Stylosanthes guianensis cv. Endeavour (stylo), at four stocking rates, 1·8, 21·87, 31·86, and 41·85 animals/ha, over 4 years on the GuadalcanalPlains, Solomon Islands.

Mean live-weight gain per head over the four stocking rates and 4 years on para pastures was 01·847, on signal pastures 01·838, and on hamil pastures 01·828 kg/head/day. Mean production per hectare at the optimum stocking rates were: para at 3.6 animals/ha, 607 kg; signal at 31·86 animals/ha, 442 kg; hamil at 21·87 animals/ha, 362 kg/ha/year.

The high stocking rates of 31·86 and 41·85 animals/ha caused the hamil pastures to decline to the stage where they were destocked in the 4th year of grazing.

Superior production on para pastures was not simply related to green dry matter (GDM) on offer. In the 1st year of grazing, GDM was highest in hamil pastures, but in the 2nd year highest in para, and in the 3rd year mean yields were similar in all pastures, but were very low at the 31·86 and 41·85 animals/ha stocking rate in the hamil pastures.

Para pastures maintained highest legume contents. The quadratic relationship between live-weight gain/head and legume content was significant over all pastures and stocking rates. Live-weight gain (LWG) per head increased up to 15% legume content, after which there was little change. Yield of green leaf, percentage green leaf, and sward bulk density did not appear to be related to LWG/head. Para pastures had lower values for all these components than the other pastures.

Chemical factors contributed to the higher animal production from para pastures. Para leaf maintained consistently higher in vitro dry-matter digestibility values. Na content of para averaged 01·812%, whereas other species were 01·801 to 01·802%, and below the critical level (01·805%) for animal intake. N and S in leaf material, and Cu in total tops were also consistently higher in para grass.

Results of this grazing trial suggest that selection of grass species on the basis of quality including dry-matter digestibility and mineral content, on ability to persist with increasing stocking rate, on compatibility with legumes, and on growth habit are more important than selection for dry-matter yield.

Studies on the effect of body weight at calving on body-weight losses during early lactation and the post-partum reproductive performance of large, medium and small buffaloes revealed that the large buffaloes (weighing more than 550 kg at calving) lost most weight (45·9 kg) and the small buffaloes (weighing less than 475 kg at calving) least weight (4·9 kg) during the first 5 months of lactation. The body-weight loss was maximal in the 1st month of lactation. The reproductive performance (measured as conception rate, number of services per conception and service period) of small buffaloes was significantly (P < 0·05) better than the large buffaloes. These results indicate that body–weight losses during early lactation are affected by the body weight at calving and these losses play an important role in influencing the post-partum reproductive performance. It is therefore suggested that, to improve the reproductive performance, the feeding regimen of buffaloes during pregnancy and after calving should be such that body-weight losses after calving are small.

Three plastic formulations of both Dursban and Dimilin were tested as controlledrelease pellets against larvae of C. pipiens and A. aegypti. Each pellet had an initial concentration of 0·116 μg/l. Results showed that Dimilin did not appear to give as high percentages of larval mortality as Dursban although in most cases a clearly delayed inhibition of adult emergence was noted. Larval mortalities of 90–100% were obtained in 3–14 (in the case of C pipiens) and 1–12 (in the case of A. aegypti) days when the second instar larvae were treated with Dursban formulations. With the Dimilin formulations no more than 31% (in case of C. pipiens) and 24% (in case of A. aegypti) larval mortalities occurred up to 13–14 days until completion of pupation.

The results obtained showed that formulation 1 (polyvinyl chloride + dibutyl phthalate + toxicant) was the most effective of the three tested ones, followed by formulations 2 (polyvinyl chloride + dibutyl phthalate + triton X·100 + toxicant) and 3 (polyvinyl chloride + dibutyl phthalate + triton X·100 + ammonium carbonate + citric acid + water + toxicant), respectively. This was so on the basis both of percentage of larval mortality and time post-treatment. The durations of effectiveness of Dursban pellets were 123, 94 and 86 days for the formulations 1, 2 and 3 respectively. However, on the basis of number of tests with over 90% larval mortality, formulation 2 gave the highest level (13 tests) followed by formulation 3 (12 tests) and finally formulation 1 (10 tests). Therefore, consideration must be given to the cumulative effect of these factors of activity when using these formulations for control of mosquito larvae. Activity indices also proved that there was no definite variation in the toxicity of both DDT-susceptible and resistant strains against these formulations. Such results were obtained with Dimilin which confirmed that formulation 3 was the most effective one. The durations of effectiveness were about 112–115 (11–67% inhibition of adult emergence), 111–113 (11–93% inhibition of adult emergence) and 102–113 (12–100% inhibition of adult emergence) days for formulations 1, 2 and 3, respectively, for the susceptible and resistant lines of C. pipiens and A. aegypti.

Two similar experiments were conducted in consecutive years using a total of 26 pregnant beef cows. The two groups of 13 cows were given 2 kg molassed sugar-beet pulp (SBP)/day for the last 16 weeks of pregnancy and 3 kg SBP/day for the first 6 weeks of lactation with oat straw ad libitum. One group was given 250 g of a fully soluble liquid supplement (LS) containing urea, phosphoric acid, calcium and sodium chloride, trace elements and vitamins poured on to the SBP. The other group received no supplementary phosphorus but was given the same amounts of supplementary nitrogen (as crystalline urea) and calcium (as calcium carbonate) together with the same amounts of sodium chloride, trace elements and vitamins as were present in the LS. The LS provided 3.7 g P/day. The overall mean phosphorus intakes of the two groups were about 5.5 g (unsupplemented) and 10.5 g P (LS)/day.

During pregnancy, reduced phosphorus intakes did not affect either the voluntary intake or digestibility of the straw. There was, however, a reduction in the blood phosphorus concentration for the cows which did not receive LS.

After calving, the voluntary straw intake, digestibility of straw organic matter, metabolizablo energy intakes and blood phosphorus concentrations of the cows which received no phosphorus supplement were severely reduced. Using the present data and that from an earlier, similar experiment, a highly significant relationship was established between blood phosphorus concentration and voluntary straw intake during the period 5.6 weeks after calving for those cows with a blood phosphorus concentration below 1.0 mmol P/l. This relationship was voluntary straw intake (kg D.M./day) = 1.55 + 5.01 × blood phosphorus concentration (mmol/1).

These results, obtained with individually fed, housed cattle, tend to suggest that a total phosphorus intake of only about 10.12 g P/day (of which 3.7 g was in the form of phosphoric acid) was adequate to maintain normal blood phosphorus concentration and voluntary straw intake and digestibility by these beef cows over the last 16 weeks of pregnancy and the first 6 weeks of lactation. This should be contrasted with the results of a similar experiment conducted earlier which clearly indicated that a daily intake of about 12 g P/day derived solely from sugar-beet pulp and oat straw was markedly inadequate.

Results of rostral tooth development determined both visually and by post-mortem radiographic examination were used to provide age ranges and median ages for stages which could be seen between 1 and 2 years old. These showed that intra-oral eruption of the permanent rostral teeth was of little value in age estimation during the second year of life. However, utilizing the stages of tooth development which could be seen radiographically the maximum age range before differentiation was 5 months (1 year 1 month from 1 year 6 months and 1 year 5 months from 1 year 10 months). Thus it appeared that rostral tooth radiography was of more use in age estimation than intraoral eruption of the permanent teeth.

A field and a glasshouse experiment were carried out to assess in winter wheat genotypes the interrelationships between stem and ear development, and to relate these to number of grains and yield. Capelle-Desprez (gai/rht2) and Hobbit ‘s’ (Gai/Rht2) were used together with four F4 lines from the cross between them. Two of the lines were homozygous for gai/rht2 and two lines homozygous for Gai/Rht2. Within each pair of homozygous lines there was a contrast between a tall and a short genotype.

There were no consistent differences in shoot apex morphogenesis between the genotypes, and, in general, similar numbers of spikelets and floret primordia were initiated in all genotypes. This contrasts with the hypothesis that genotypes based on Norin 10 (Gai/Rht2) have a fundamentally different pattern of ear morphogenesis. The main differences between genotypes were in dry-matter partitioning to stem and ear prior to anthesis and these were associated more consistently with the dwarfing gene than with height per se. Gai/Rht2 genotypes partitioned more dry matter to the ear during its development and less to the stem and this was reflected in greater ear weight at anthesis, more fertile florets and grains per spikelet, a higher harvest index and higher grain yield than the gai/rht2 genotypes. Although similar numbers of floret primordia were initiated in all genotypes, assimilate partitioning during development determined the proportion which developed into fertile florets at anthesis.

Five experiments, involving 37 varieties, were carried out over three seasons to estimate the increase in yield potential in spring barley achieved by plant breeding during the last 100 years. Most of the important spring barley varieties grown in Britain between 1880 and 1980 were represented. In three experiments disease was controlled by a fungicide while in the other two experiments fungicide application was a main treatment. To prevent yield loss due to lodging, plants were supported as a main treatment in two trials.

In all experiments most of the modern varieties yielded more than the older ones. The genetic gain in yield was 0·39% per year during the 100-year period and 0·84% per year between 1953 and 1980.

Modern varieties had higher grain yields, shorter straw, and higher harvest index denned as the proportion of grain dry weight to total above-ground dry weight; more of the tillers they produced survived to give ears. There was a weak association between biological yield (total above-ground dry weight) and grain yield.

It is suggested that although much of the improvement in yield described here could be attributed to increased harvest index, the scope for further improvement in this character may be limited. Further yield improvements might be achieved by combining high biological yield with high harvest index.

Field experiments were conducted for three seasons, 1971–2, 1972–3 and 1973–4 to study the effects of nitrogen fertilizer and seed rate and their interactions on grain yield and its components and attributes of growth of two wheat varieties, Giza 155 and Mexipak. The semi-dwarf Mexipak was found to be more responsive to nitrogen application than the taller Giza 155 in a number of aspects, namely, grain yield per unit area of land, the number and weight of grains per ear, the dry weight per ear and dry weight of ears/m2. The numbers of spikelets and grains per ear of both varieties decreased linearly with an increase in seed rate. The 1000-grain weight was not affected in both varieties by either seed rate or N fertilizer.

Variety × nitrogen, variety × seed rate and nitrogen × seed rate interactions were significant; the variety × nitrogen × seed rate interactions were not significant. Mexipak was found to have a definite optimum seed rate of 192 kg/ha at an optimum N level of 129kgN/ha for maximum grain yield. Giza 155 was less responsive to changes in seed rate and therefore its optimum seed rate was not as definite as that for Mexipak. Evidence presented here suggests that wheat varieties of different growth habits grown in the Sudan should receive differential treatments when the policies of setting optimum seed rates and nitrogen fertilizer rates are considered.

Grain yield of both varieties was positively correlated with total dry weight of shoot at heading.